Vehicle applications using compressed natural gas systems often operate in variable environmental conditions and under changing operational modes. Changes in ambient temperature and changes in operational modes (idling, moving, loading, and the like) may effect the density of the fuel delivered to the engine by high pressure direct injection. Stable and consistent engine power output may be improved by controlling the fuel mass of the compressed natural gas delivered to the engine. Consistent fuel mass delivery provides a combustion environment that allows for stable power generation regardless of changing environmental or operational conditions.
U.S. Pat. No. 7,182,073 issued Feb. 27, 2007 (the '073 patent) discloses a liquefied petroleum gas injection engine system on a vehicle. The system disclosed seeks to lower emissions by reducing leakage of fuel into the intake system of the engine after the engine has been in an off condition. The '073 patent discloses an engine control management system electronic control unit that controls the injection time and injection rate of the liquefied petroleum gas injected through the injector depending on the traveling conditions of the vehicle, more specifically whether the fuel system receives natural cooling by outside air while the vehicle is moving or whether the vehicle is stopped and natural cooling of the air is unavailable. This type of system has drawbacks because the temperature of the fuel delivered may vary widely. A better system is needed.